The articles and essays in this blog range from the short to the long. Many of the posts are also introductory (i.e., educational) in nature; though, even when introductory, they still include additional commentary. Older material (dating back mainly to 2005) is being added to this blog over time.

Thursday, 23 July 2015

Peter Murphy Rewrites the a Priori/a Posteriori Distinction

Dual Epistemic
Justification

Peter
Murphy’s simple point in this paper is that nonbasic beliefs can be
justified by both experiential and nonexperiential justifiers; not
just either one or the other. He's concerned with the cases

“in
which neither the nonexperiential justifier nor the experiential
justifier would suffice on its own, in the absence of the other, to
justify the non-basic belief”(2).

What
would happen if one of the justifiers were absent? Murphy writes:

“In
the absence of either justifier, one of the basic beliefs would be
unjustified and, as a consequence, so too would the non-basic belief.
The two justifiers function as cocontributors…”(2)

Despite
that, Murphy’s prime purpose is to “rewrite” Kant’s strict
binary distinction between a priori and a posteriori
beliefs. He argues that in the case of the justification of a
nonbasic belief which has both a nonexperiential and an experiential
justifier, Kant classified the resultant belief a posteriori.

A
Kripke Case

Murphy
gets his point across by offering us an example which is taken from
Saul Kripke. Take the following argument-frame:

(1) (H = P) ⊃ □(H =
P).

(2) (H = P)

(C) ∴ □(H = P)

Murphy
says that Kripke takes (1) above to be known a priori. That
is, if H and P are identical, then they are necessarily
identical. The identity of H and P in this case, however, was only
known (or discovered) a posteriori.

So
what about (C) - the conclusion? Is that known a priori or a
posteriori? More relevantly, is the whole argument a priori or
a posteriori? Murphy argues that Kripke follows Kant on this.
He takes (C) to be justified or known a posteriori because the
identity of H and P (in (2) above) was only known experientially (or
through observation). Thus the whole argument, as well as the
conclusion, is classified a posteriori, despite it dealing
with a necessary identity.

Clearly,
from what I've written, Murphy has a problem with Kripke’s
classification. The basic point is that although the necessary
identity of H and P only came to be known a posteriori, the
modal conditional, (H=P) ⊃ □(H=P), still holds true without
experience. That is, it's known to be necessarily true a priori.
So in the Kripke case, and in the case of other nonbasic beliefs, we
have what Murphy calls epistemic co-contributors.

Murphy
gives another example of the phenomenon of epistemic co-contribution.
Firstly we have the a priori part:

ii) The same belief is
partly a posteriori justified by her recent experience
counting and recounting groups of blocks

Murphy
also gives us a similar example.Again, firstly we have the a
priori part:

i) A new logic student
might have a marginally reliable a priori insight into
DeMorgan’s Rule.

Then
the a posteriori part:

ii) He might also base
his belief in DeMorgan’s Rule on his marginally reliable roommate’s
testimony that DeMorgan’s Rule is true.

A Priori
Inference and Dual Justification

Murphy
also highlights the case of inference.

Laurence
BonJour makes much of inference in his apriorist criticisms of the
Quinean “web of belief” thesis. (The beliefs in this web may well
be empirical; though what about the links between them?) According to
Murphy, BonJour also “proposes that acts of inferring are a
distinct kind of justifier” (3).

What
Murphy (or BonJour) is interested in is this move (or link) from
belief to belief. Even if the move is from nonbasic and experiential
beliefs to other beliefs, that link still requires an epistemic
description, explanation and justification. More relevantly, the
inference from belief to belief (or from beliefs to beliefs) needs to
be justified. This will result in dual justification. Murphy argues
that “there will be cases where the inference is justified one way
and the relevant premise-beliefs are justified another way” (3).
That is, the premise-beliefs may be justified a posteriori;
though their links to - or the inferences from - other beliefs
will be a priori in nature. Again, Murphy makes the conclusion
that if we

“[t]ake
away either the a posteriori
justified belief or the a priori
justified inference… the person’s conclusion-belief would be
unjustified” (3).

In
Kant’s book, according to Murphy, we can say that

“[s]ince the
conclusion-belief is dependent on an experiential justifier for its
justification, Kant has us put it in the a posteriori category”
(3).

That
is, Kant says that the conclusion-belief is experiential or a
posteriori in nature, despite the fact that it was derived from a
process which is a priori (even in that case when the
premise-beliefs were also a posteriori).

Murphy
also detects an ‘asymmetry’ in Kant’s account. Thus:

i) To be a posteriori
justified, a belief only needs to partially depend on
experiential justifiers.

However,
an a priori justified belief doesn't get the same treatment
from Kant. Thus:

ii) “To
be a priori
justified, it is not enough that a belief partially depend on
nonexperiential justifiers for its justification – it must
exclusively depend on
nonexperiential justifiers.” (3-4)

Murphy’s Weak
Rationalism

Where
does Murphy stand on the general empiricist/rationalist debate which
underpins the issues just discussed?

He
detects four positions:

Two
Radical Positions:

Radical empiricism:
this position denies that there are any non-experiential justifiers
and insists that all justified beliefs are justified aposteriori.

Radical rationalism:
this position denies that there are experiential justifiers and
insists that all of our beliefs are justified a priori. (4)

Two
Moderate Positions

Strong rationalism:
this position argues that some of our justified beliefs are a
priori justified.

Weak rationalism:
this position argues that there are non-experiential justifiers, but
restricts their justifying power to beliefs that are justified in a
mixed manner.